I use foobar2000 on android, not sure it does what you want but it does import .m3u playlists
I also like fossify music player, works with playlists but not sure about scanning like you say https://f-droid.org/packages/org.fossify.musicplayer
Ive been using opentune (from fdroid) that i use for youtube music (you have to log in to a youtube accnt, but it lets you download off youtube), this also scanned my phone for files but again not sure about playlists
i mostly just listen to albums because i am a very sophisticated person :p